MozBackup is not being developed anymore. There are known issues and
there is no time on my side to fix all issues and develop new features. Use MozBackup only on your risk.
Thanks for understanding. Source code is available on GitHub.

Must I uninstall a previous version of MozBackup before installing a new version?

Yes, it's recommended.

Can I change default backup filename?

Yes. See config file backup.ini in program folder.

Is Lightning extension supported?

Yes.

Can I use MozBackup for synchronization between two PCs?

I don't think this is a good idea. If you use Firefox try Firefox Sync
which is better for such task. If you use Thunderbird try to think about having your mails on server and access to them via
IMAP protocol. Familiar solution you can have for contacts.

Issues

What can I do if I have a problem with restoration of backup?

Rename PCV file to ZIP and extract manually. Visit MozillaZine KB where you can find
how to do it.

After restoration of my mails I don't see some mails in folder. What can I do?

MozBackup detects another version of Mozilla application. How to fix it?

You can ignore this - info about version is only informative. MozBackup gets this information from
Windows registry. So if you have old information there, MozBackup shows this. Program backups/restores profiles
and for this, it's not important that the version of applications is completely accurate.